Merck says the recall covers all four dose strengths and every batch distributed since Liptruzet was launched last May.

Merck, the world's third-biggest drugmaker, says some of the foil pouches holding the pills may allow air and moisture inside. Merck says there's a remote chance that could decrease the drug's effectiveness or otherwise change its properties, but that the recall is not due to any reports of patients being harmed.

The Whitehouse Station, N.J., company says patients can continue taking any Liptruzet they have and should consult a doctor before stopping therapy. Merck plans to get Liptruzet back on the market as soon as possible.